Electrostatic-capacitance-type acceleration sensor

Abstract

In an electrostatic-capacitance-type acceleration sensor, water, etc. penetrating into a sealed space incorporating an acceleration detector having a movable electrode 6 , and sticking of the movable electrode 6 to a cap 8 due to static charge accumulated on the cap 8 during the anodic bonding being performed are prevented. A conductive shielding film 9 that can be extendedly transformed on the entire inner face of the cap 8 constituting the sealed space is provided, which is not only extendedly arranged so as to be sandwiched between a bonding frame 7 and the cap 8 , but also electrically connected to the movable electrode 6 ; thereby, even if unevenness exists on the surface of the bonding frame 7 , not only sufficient anodic bonding between the bonding frame 7 and the cap 8 becomes possible, but also the electric field due to the static charge accumulated in the cap 8 can be shielded.

1. An electrostatic-capacitance-type acceleration sensor comprising:
 a substrate including an acceleration detector having a movable part for detecting an acceleration; 
 a bonding frame fixed on the substrate so as to surround the acceleration detector; 
 a cap provided on the substrate, a face of the cap opposed to the substrate being constituted by a peripheral region affixed to the bonding frame, and in addition to the peripheral region, a central region; and 
 a conductive shielding film formed at least on an entire surface of the central region of the cap, the shielding film electrically connected to the movable part, wherein 
 a void is formed between the bonding frame, the cap, and the conductive shielding film such that a part of the bonding frame forms a first wall of the void, a part of the cap forms a second wall of the void, and a part of the conductive shielding film forms a third wall of the void, the cap and the bonding frame being joined at mutually extending portions between the void and exterior sides of the cap and the bonding frame. 
 
     
     
       2. An electrostatic-capacitance-type acceleration sensor as recited in  claim 1 , wherein the shielding film is formed extending onto a surface of the peripheral region. 
     
     
       3. An electrostatic-capacitance-type acceleration sensor as recited in  claim 2 , wherein the shielding film includes a first portion having a first thickness, and a second portion having a larger thickness than the first thickness and provided on the central region. 
     
     
       4. An electrostatic-capacitance-type acceleration sensor as recited in  claim 2 , wherein a recess for accepting the shielding film is formed either in the bonding frame or in the cap. 
     
     
       5. An electrostatic-capacitance-type acceleration sensor as recited in  claim 2 , the cap having a support protruding from the central region, wherein the shielding film and the movable part are electrically connected together through the shielding film being formed on a surface of the support. 
     
     
       6. An electrostatic-capacitance-type acceleration sensor comprising:
 a substrate including an acceleration detector having a movable part for detecting acceleration; 
 a bonding frame fixed on the substrate so as to surround the acceleration detector; 
 a cap provided on the substrate, and composed of a peripheral region, whose face faces the substrate, fixed to the bonding frame and a central region other than the peripheral region; 
 a conductive shielding film formed at least on an entire surface of the central region of the cap, wherein a void is formed between the bonding frame, the cap, and the conductive shielding film such that a part of the bonding frame forms a first wall of the void, a part of the cap forms a second wall of the void, and a part of the conductive shielding film forms a third wall of the void, the cap and the bonding frame being joined at mutually extending portions between the void and exterior sides of the cap and the bonding frame; 
 a first external electrode connected to the movable part; and 
 a second external electrode connected to the shielding film, wherein 
 the first external electrode and the second external electrode are arranged to be electrically connectable to each other. 
 
     
     
       7. The electrostatic-capacitance-type acceleration sensor as recited in  claim 1 , wherein the void has a depth equal to or smaller than a thickness of the conductive shielding film. 
     
     
       8. The electrostatic-capacitance-type acceleration sensor as recited in  claim 1 , wherein the void is formed entirely along the bonding frame.